1/*
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3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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24
25#ifndef SHARE_UTILITIES_QUICKSORT_HPP
26#define SHARE_UTILITIES_QUICKSORT_HPP
27
28#include "memory/allocation.hpp"
29#include "runtime/globals.hpp"
30#include "utilities/debug.hpp"
31
32class QuickSort : AllStatic {
33
34 private:
35 template<class T>
36 static void swap(T* array, size_t x, size_t y) {
37 T tmp = array[x];
38 array[x] = array[y];
39 array[y] = tmp;
40 }
41
42 // As pivot we use the median of the first, last and middle elements.
43 // We swap in these three values at the right place in the array. This
44 // means that this method not only returns the index of the pivot
45 // element. It also alters the array so that:
46 // array[first] <= array[middle] <= array[last]
47 // A side effect of this is that arrays of length <= 3 are sorted.
48 template<class T, class C>
49 static size_t find_pivot(T* array, size_t length, C comparator) {
50 assert(length > 1, "length of array must be > 0");
51
52 size_t middle_index = length / 2;
53 size_t last_index = length - 1;
54
55 if (comparator(array[0], array[middle_index]) > 0) {
56 swap(array, 0, middle_index);
57 }
58 if (comparator(array[0], array[last_index]) > 0) {
59 swap(array, 0, last_index);
60 }
61 if (comparator(array[middle_index], array[last_index]) > 0) {
62 swap(array, middle_index, last_index);
63 }
64 // Now the value in the middle of the array is the median
65 // of the fist, last and middle values. Use this as pivot.
66 return middle_index;
67 }
68
69 template<bool idempotent, class T, class C>
70 static size_t partition(T* array, size_t pivot, size_t length, C comparator) {
71 size_t left_index = 0;
72 size_t right_index = length - 1;
73 T pivot_val = array[pivot];
74
75 for ( ; true; ++left_index, --right_index) {
76 for ( ; comparator(array[left_index], pivot_val) < 0; ++left_index) {
77 assert(left_index < length, "reached end of partition");
78 }
79 for ( ; comparator(array[right_index], pivot_val) > 0; --right_index) {
80 assert(right_index > 0, "reached start of partition");
81 }
82
83 if (left_index < right_index) {
84 if (!idempotent || comparator(array[left_index], array[right_index]) != 0) {
85 swap(array, left_index, right_index);
86 }
87 } else {
88 return right_index;
89 }
90 }
91
92 ShouldNotReachHere();
93 return 0;
94 }
95
96 template<bool idempotent, class T, class C>
97 static void inner_sort(T* array, size_t length, C comparator) {
98 if (length < 2) {
99 return;
100 }
101 size_t pivot = find_pivot(array, length, comparator);
102 if (length < 4) {
103 // arrays up to length 3 will be sorted after finding the pivot
104 return;
105 }
106 size_t split = partition<idempotent>(array, pivot, length, comparator);
107 size_t first_part_length = split + 1;
108 inner_sort<idempotent>(array, first_part_length, comparator);
109 inner_sort<idempotent>(&array[first_part_length], length - first_part_length, comparator);
110 }
111
112 public:
113 // The idempotent parameter prevents the sort from
114 // reordering a previous valid sort by not swapping
115 // fields that compare as equal. This requires extra
116 // calls to the comparator, so the performance
117 // impact depends on the comparator.
118 template<class T, class C>
119 static void sort(T* array, size_t length, C comparator, bool idempotent) {
120 // Switch "idempotent" from function paramter to template parameter
121 if (idempotent) {
122 inner_sort<true>(array, length, comparator);
123 } else {
124 inner_sort<false>(array, length, comparator);
125 }
126 }
127};
128
129
130#endif // SHARE_UTILITIES_QUICKSORT_HPP
131